Hi Pat
Oops, the mail threads somehow split into two and we are repeating arguments:-(
I have just posted a mail:
http://www.w3.org/mid/4725B658-B2B1-49EA-924C-DF0A1386F868@w3.org
before getting to this thread and which, I believe, got to the same conclusion except that yours is properly spelled out:-)
All this to say: +1:-)
Ivan
On Aug 8, 2013, at 06:46 , Pat Hayes <phayes@ihmc.us> wrote:
>
> On Aug 7, 2013, at 12:54 PM, RDF Working Group Issue Tracker wrote:
>
>> RDF-ISSUE-140 (dataset-comparison): RDF Dataset Comparison (Ivan Herman) [RDF Concepts]
>>
>> http://www.w3.org/2011/rdf-wg/track/issues/140
>>
>> Raised by: Ivan Herman
>> On product: RDF Concepts
>>
>> I have a question/comment on this:
>>
>> [[
>> 4.1 RDF Dataset Comparison
>>
>> Two RDF datasets (the RDF dataset D1 with default graph DG1 and named graph NG1 and the RDF dataset D2 with default graph DG2 and named graph NG2) are dataset-isomorphic if and only if:
>>
>> â€¢ DG1 and DG2 are graph-isomorphic;
>> â€¢ For each (n1,g1) in NG1, there exists (n2,g2) in NG2 such that n1=n2 and g1 and g2 are graph-isomorphic;
>> â€¢ For each (n2,g2) in NG2, there exists (n1,g1) in NG1 such that n1=n2 and g1 and g2 are graph-isomorphic.
>>
>> ]]
>>
>> A graph name can now be a blank node. Wouldn't it be appropriate to use the 'M' mapping of section 3.6 for the graph names, too? Or are we deliberately silent on this?
>
> We need to do *something*, as the above definition is now wrong. For example, it says that these are isomorphic:
>
> { {_:x rdf:type ex:graphsIlike .}
> _:x {ex:a ex:b ex:c} }
>
> { {_:y rdf:type ex:graphsIlike .}
> _:x {ex:a ex:b ex:c} }
>
> which is incorrect.
>
> Yes, the best way to fix this would be to describe it in terms of the M mapping, IMO. Here is a stab:
>
> Two RDF datasets D1 (with default graph DG1 and named graph set NG1) and D2 (with default graph DG2 and named graph set NG2) are dataset-isomorphic if and only if there is a bijection M between the nodes, triples and graphs in D1 and those in D2 such that:
>
> 1. M maps blank nodes to blank nodes
> 2. M is the identity map on literals and URIs
> 3. For every triple <s p o>, M(<s, p, o>)=<M(s), M(p), M(o)>
> 4. For every graph G= {t1, ...1n}, M(G)={M(t1), ..., M(Tn)}
> 5. DG2 = M(DG1)
> 6. <n, G> is in NG1 if and only if <M(n), M(G)> is in NG2.
>
> I think this is correct and states the conditions about as neatly as possible.
>
> Pat
>
>
>>
>> Ivan
>>
>> [http://lists.w3.org/Archives/Public/public-rdf-wg/2013Aug/0008.html]
>>
>>
>>
>>
>
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----
Ivan Herman, W3C
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